1. Field of the Invention
This invention relates to high velocity projectile launchers or guns as well as an explosive charge assembly specifically suited therefor. In particular, the present invention relates to a gun which utilizes an explosive charge assembly which utilizes low molecular weight gas or plasma to drive a projectile.
2. Description of the Related Art
Since about the 14th century, the term "gun" has commonly been used to represent a device which includes a long tube open at one end, the muzzle, and, closed at the other end, the breach. The projectile to be fired is placed part way down the tube from the breech, leaving a volume, the chamber, which holds the propellant. After ignition, the propellant combusts rapidly filling the chamber with propellant gas at high pressure and temperature. This released energy created by the ignition of the propellant is used to accelerate both the gas created by the detonation of the propellant and the projectile. In spite of improvements being made in propellants and materials for forming the muzzle and breech, the utilization of the products of the deflagration or detonation as the propelling gas has led to a limit on muzzle velocity (e.g., 1.4.about.1.8 km/sec) which is inadequate for many desired uses.
The realization that inherent high sound speed in light gases (especially, high temperature light gases) could lead to higher launch velocities led to the development of "light gas guns" such as that disclosed in U.S. Pat. No. 3,186,304. A light gas gun uses a low-molecular weight gas such as hydrogen which is compressed to high pressures and temperatures for use as a driver gas to accelerate projectiles to high velocities. Single and two-stage light gas guns capable of accelerating small projectiles to velocities in excess of 10 km/sec were developed in the late 1960's. The light gas gun technique centers around converting a substantial portion of the chemical energy from an explosive charge into the internal energy of a light gas. Strong shocks generated by the collapse of a light gas containment tube or by compression of a conventional piston produce high energy densities in light gases and lead to the increase in projectile velocities.
A single stage light gas gun utilizing a thin walled metal containment cylinder surrounded by a chemical explosive is illustrated in U.S. Pat. No. 3,465,638. Upon detonation, the thin wall of the containment cylinder accelerates inward forming a conical "piston" that compresses the gas.
A two stage light gas gun is disclosed in U.S. Pat. No. 3,311,020 and operates in a manner similar to that of the single stage light gas gun except for the use of a conventional piston as the means to compress the low molecular weight gas.
A modified form of the light gas gun, commonly referred to as a wavegun, is disclosed in U.S. Pat. No. 4,658,699. The wavegun involves an initial detonation which causes a piston and shock wave to move forward compressing a light gas. The placement of a diaphragm at the end of the light gas chamber results in a deflection of the piston and a compression of the still-burning propellant. This process continues through several compressions and deflections with the number of cycles depending on the strength of the diaphragm and the type of propellant. By multiple compressions, higher temperatures and pressures are achieved than in the standard two-stage light gas gun. An advantage of the wavegun is that it allows a smaller pump tube and lighter piston than the standard two-stage light gas gun.
Despite the increase in projectile velocity obtainable by the various light gas guns, the use of these devices is restricted due to the light gas guns typically having pump tubes 10 to 20 meters in length and pistons typically weighing between 1 to 8 kg. These structural attributes of the standard light gas guns make them inappropriate for many uses such as use as a field weapon. In addition, although light gas guns can accelerate projectiles (about 5 kg) to velocities of 5 km/sec, they are difficult to mechanize and are limited to slow rates of fire.
The wavegun has overcome some of these problems with a pump tube that is typically less than 1 meter long and a piston mass of less than 1 kg, but is felt not to be capable of achieving 3 km/sec with a 1.4 kg. projectile.
A problem common to both the two-stage light gas gun and the wavegun is the inefficiency of having to drive a fairly massive piston to achieve compression of the light gas. Similarly, the problems presented by the single stage light gas gun such as U.S. Pat. No. 3,186,304 include the problem of achieving a suitable gas temperature and pressure within the gun that provides both high velocity projectiles as well as adaptability for use in the field.